Filtering process and apparatus



Get. 21. 1924.

J.F. WAIT FILTERING PROCESS AND APPARATUS Filed-Fem?. 1920 2 sheets-sneer 1 Prisa/Hi fai att-www3 ct. Q21. 1924. 1,512,321

J. F. WAIT FIL'I'ERING PROCESS AND APPARATUS Filed Feb. 2 1920 2 Sheets-Sheet. 2

fw" y JW 11m/minimi l attoqwg Patented Octagl, 1924.

JUSTIN F. WAIT, F BUFFALO', NEW YORK.

FIITERING PROCESS AND APPARATUS.

Application led February 2, 1920. Serial No. 355,592.'

allied processes, and to apparatus used in -the performance thereof,- and especially to that type known as pressure filters` The subjects of the present invention are particularlyapplicable to, or useful in, wfilters of the rotary type, but may be used in connection with filters of other types, as found X- desirable. v I One object of the invention is to permit the use in the filter of special atmospheres of vapors or gases; another object is to provide for the use of higher pressures .than ordinary; anotherobject is to provide for the recovery of a maximum amount of volatile solvents by re-circulating the sol-vent, thus also preventing undesirable deco-mpcsition and crystallization-.of crystals and impurities in the l*cake first formed, due to evaporation of theretained solvent. EX- amples of this lare such cases as the filteringr for removal of solids from a volatile liquid in which extracted oil or wax has been dissolved by treatment with -an organic solvent, or of certain chemicals which might be purified in `an organic solvent. These and other objects are accomplished by the methods and apparatus hereinafter described.

Heretofore, filtration has ordinarily been accomplished, in the' rotary type of pres- 40 sure filters, by-rotating a gang of filters in an open trough' containing the material to be filtered, and these filters pick up the solid material in the form of a cake which is afterwards washed, and .then scraped from the filters, the operation being conducted in the air, the filtrate being drained from the precipitate by vacuum drawn through a hollow shaft. which carries the filter units.

In the separation of a precipitate from a liquid, it is frequently vfound that the cake formed during the filtration is altered by Contact with air. This is equally true when a substance is being washed or lsaturated by the oxygen of the air.

lwith a liquid. In suchcases it is desirable to maintain an atmfosphere of inert or protective gas or vapor about the drum or filter element and the material being filtered.'

An example of this is the case of the reduc'- tion of an organic'compound containing a nitro group, the lcorresponding amido compound being easily decomposed or altered In such a case it is advisable to surround the filter elev ments with an atmosphere of hydrogen for example. In lorder to obtain a high economy 1n the amount of hydrogen used it is essential to recover the-hydrogen from the low pressure side of the filter and pump it back to the high pressure side. In extreme cases it may be essential lto maintain positive pressures on 4bothsides of the filtering medium in order to prevent infiltration of. air from the atmosphere, due to leakage. In such acase. small amounts of hydrogen will be added from time to time, in amounts equivalent to that whichl is dissipated by leakage, or discharged with the product handled. l

' Also, in an ordinary vacuum rotary drum filter the' rate of filtration is Vabsolutely limited to the capacity of that filter operating under a perfect vacuum, -equal to a pressure of approximately fifteen pounds per squareinch. In order to greatly increase the rate of filtration of such'a filter, as well as to permit the filtration to be ef-V fected in a desired atmosphere, I surround the filter by a stationary vair tight chamber to which a positive pressure in excess of atmospheric pressure may be applied. .By this means the rate of filtration may be greatly increased and the resulting quality improved. i

During the process it maybe desirable to wash or spray the; material on the drum,-

`to which end a 'number of spray nozzles or' the like may be placed Within the chamber.

In treating materials by washing or satu- *rating -them by means of a volatile solvent ferred to, and theair, vapors or gases passr ing through the. filter are pumped backfrom the low pressure side to the high pressure side, and into thefchamb'er, this pumping being necessary in. order to maintain the differential pressures essential to the process of filtration.

By such a closed system it is possible to use solvents and /liquids ver f easily volatilizfed, and liquids boiling at room temperature and at pressures less than atmiospheric may be used for crystallization and washing purposes. The amount of pressure which l impose will be sufficient to raise the boiling point of the liquid above the temperature of the operation. Y l

Hence my process involves or includes the operation of the filter in a closed chamber containing an inert or special atmosphere of vapors or gases, as well as the use of higher pressures, and the re-circulation of such vapors or gases from the low pressure side to the high pressure side of the apparatus.

In order to obtain a filter cake of low liquidcontent it is frequently advisable to employ an atmosphere of warm air, vapor or gas, and in this case the air or gas applied to thehigh pressure side is previously heated, or heated at or near the point where' it is drawn through the cake. For'this pur pose l either place heated units inside the casing or heat the gas beforev it enters the chamber and direct itsv flow to the desired place.A

In re-circulating gases or vapors from the low pressure side' of thel filter to the high pressure'side'its/is desirable to separate as much of thel liquids as possible. This I do by placing a separator or condenser or both in the line` betweenthe pump and the chamber. vA heat exchanger is desirableunder some conditions, to warm the vapors or gases after passing through such condenser or separator, and the heat used" maybe obtained conveniently from the discharged vapors of the 'filter or the dischargedliquids.

Although reference is made above to filters of the rotary drum type, itis possible toapply the methods involved-that is, inert gases, vapors, higher pressures for the use of volatile components, positive pressures on both sides of the filter medium, circulation and recovery of the samef gasesior .vaporsto other types or classes-.of filters, such as an ordinary single plate pressure filter. Hence the application of the invention in many of its aspects is not limited to any particular type of filter.

Apparatus suitable for performing the process disclosed is shown in the accompanying drawing. Figs. 1( and 2 are elevations partly in section of a rotary drum filter.

igs. 3, 4, 5, 6 and 7 are diagrams of different types of filters and connections in which the processmay be employed.

Referring to Figs. 1 and 2, A indicates a casing or chamber entirely surrounding the filter drum D' and adapted to contain the gases or vaporsunder pressure. The drum may be of any known or suitable construction and will be covered with suitable cloth or other filtering material. P is a scraper for removing the cake from the drum, and W is a screw tapped through the casing and connected to the scraper for adjusting the same.` The scraper delivers the cake to a screw conveyer R to remove the same from the casing and discharge it to any desired place; the cake being discharged by the conveyer pipe for example into a receiver under approximately the same pressure as the filter, thereby preventing loss of gas through the conveyor.

The drum will be divided into a plurality of sections as well known in the art, to each of which different suctions or pressures may be applied, by means of a known distributing valve V. The casing is preferably divided into two sections joined at bolted flanges L. T is an inlet for the gases or vapors with which the drum is surrounded: I is the inlet for the material to be filtered which will be supplied under the same pressure as that in the filter; H is a hollow revolving shaft containing outlet pipes from the sections of the drum, connecting with the distributing valve through which pipes and valve the filtered liquid is drawn off7 in a known manner; and Y is a spray pipe for the washing fluids. These parts may be `adaptedfrom known filters and require no extended description, the gas tight outer chamber being however a new feature.

N is a window or sight,glass in the casing, since in the construction of such a machine it is highly desirable to be able to determine the depth of liquid within the chamber and to inspect the cake as it is delivered by the drum, and at other times during the cycle.

It will be understood that the druin is revolved, and under vacuum will pick up the precipitate in the form of a cake which will first be washed by the spray and then dctached by the scraper, the distributing valve V regulating the pressures at the different points in the cycle. Suitable contro] of the filter is secured by constructing the valve V so that the pressure on the sections of the filter may be so controlled that different. ser tions will have different pressures during different periods of operation. the pressure on one side being the lower during the different periods ofthe treatment. It may at times be desirable to reverse the pressure at a certain period to aid in discharging the cake when the treatment is complete. this being a known operation.

lt may be stated that if a small pressure llt) in excess of atmospheric pressure or a pressure equal to atmospheric pressure is carried on the low pressure side of the filter it will be possible to use liquids with low boiling points` and prevent their evaporation while Maasai in -the cake, thus preventing undesirable crystallization in the cake. One of the main reasons for adjusting the pressure inthe individual sections on the 10W pressure Side of arotary drum filter is that it is desirable to have less pressure during the Washing period and during that part of the drying period in which the cake is apt to crack.

Figs. 3 and 4 illustrate the application' of the process to a rotary filter, 'and show the return circulation from the valve V through a separator S. to remove the liquids, I the pump P returning the vapors or gases to the casing A through the inlet at T.

Figs. 5 and 6 .illustrate ordinarysingle plate filters, with return of gases or vapors, A being the pressure chamber above the filter medium M, Z- the low pressure chamber from which the gases are drawn by a pump P and forced through a condenser C, separator S, receiver and heater R back to the inlet T, I and I1 being inlet and outlet for material respectively.

Fig. 7 may be conveniently read in con'- nection with a rotary drum filter of the type shown in Figs. 1 and 2 having diEerent pressure sections, with a distributing valve V the dierent outlets from which are piped as indicated at X to different-receivers and heaters R1, R2, R3 and R4 and thence to a pump P and separator S, the gases being returned to the filter inlet T. Thelines are. provided with pressure regulating valves Gr respectively, to vary the suction filtercake,

- l l n cipitate in the filter and returnmg sald uid l pressure on the respective sections.

The invention may be embodied 4or practiced in machines. of various other types, and no limitatiomin this respect is implied. Also selected features or steps of the process may be employed, Without the use of others, and be Within the scope of the inventi0n,.dependinglargely on the results desired and the-nature of the material being treated.

By pressure filtering, in th1s specification,

is meant processes of filtering in which the flow of liquid through a membrane, cloth or other medium is made positive by the application of pressure on one side of that medium in excess of the pressure existing onthe other side. v

1. In pressure filtering `for the separation of solids from liquids, the method comprising conducting the filtration in a reducing atmosphere with respect to the filter cake.

2. In pressure filtering employing a volatile solvent for the purpose of treating the the method comprising forclng a gaseous fluid and a solvent through the reand the solvent absorbed thereby to the-filter for re-circulation therethrough. y

3. In pressureefiltering for the separation of solids from liquids, the method comprising excluding air from the interior of the filter and maintaining therein a non-oxidizing atmosphere Avwith respect to the filter I cake.

4. In pressure filtering, the method comprising filtering, Washing the filter cake with a volatile solvent, subjecting it tothe ressure of a gas, and returning the gas that passes through the filter to the high pressure side of the filter for successive operations.

5. In pressure filtering, the method comprising excluding air from the filter, Washing the filter cake in the filter by a solvent,

recoveringthe solvent by separation fromV dissolved substances and returning the solvent tothe lter.

SFIn pressure ltering for the separation of sol-ids from liquids, the method comprising surrounding the filtering medium and the lter cake, during filtration, with an atmosphere of hydrogen under pressure, and returning the hydrogen from the low pressure to the high pressure side of the filtering medium.

- 7. In pressure filtering for the separation of solids from liquids, the method comprising, circulating a gaseous solvent fluid through the filter cake from the high pres` sure side to the 10W pressure side and back to the high pressure side, and separating the liquid portion of the fluid from` the gaseous portion thereof before its return to thel high pressure side.4

8. In a pressure filter, the'combination of a closed filtering chamber, filtering elements therein havin sections for different pressures, a distrlbuting valve communicating with said sections, pipes communicating with said valve and each provided with a pressure regulating valve, a return pipe lciable quantities of alr.

i In testimony whereof, I hereby aiiix my signature in presence of two Witnesses.

JUSTIN F. WAIr. Witnesses:

C. A. K. Pls'rELL, -FRANK C. IMBU, JR. 

